Transparent coatings of poly(methyl methacrylate) homopolymers and copolymers are known and applied to thermoplastic substrates, particularly, polycarbonate substrates, to impart UV light stablility to the finished article. However, it has long been a problem with such coatings, that a single formulation could not be discovered to provide desirable properties in all areas, i.e., including high gloss, retention of gloss after weathering, heat distortion temperature, elongation at break, UV stability, and resistance to microcracking. Particularly, microcracking with aging and exposure to weather has been a serious problem in such coatings.
U.S. Pat. No. 3,582,398 assigned to the same assignee as the present invention discloses the use of the polyacrylates in general and specifically the polymethacrylates as coatings on polycarbonate substrates to enhance optical properties. These coatings are known on occasion to microcrack and degrade with age and weathering.
Therefore, it is an object of the present invention to provide thermoplastic articles with a solvent and abrasion resistant methyl methacrylic coating, which coating has improved resistance to microcracking yet maintains desirable heat distortion properties, transparency, high gloss, good retention of gloss after weathering, desirable elongation at break, and excellent UV stability.
It is yet another object of the invention to provide polycarbonate articles with the same polymethylmethacrylic coatings and properties.
It is still another object of the present invention to provide a method for protecting thermoplastic substrates from UV degradation with improved weathering properties in the protective coating used to accomplish the same.